1. Field of the Invention
The present invention relates to image processing to provide a non-strained image from the data of an image pick-up device.
2. Description of the Related Art
The image pick-up device used in the prior art is typically a CCD camera which can pick up an object, process the data of the picked-up image (which will be referred to "pick-up data") and detect the position of the object. Three-dimensional vision is particularly important in an intelligent robot which self-supportingly behaves while judging its surrounding situations. In such an intelligent robot, it is desired to recognize the exact three-dimensional position of the object from the pick-up data obtained by the image pick-up device.
The utilization of the CCD camera greatly reduces the strain in a picked-up image, in comparison with the other image pick-up devices of the prior art. When the resulting pick-up data is processed, the position of the object can very exactly be recognized. In other words, the position of the object can be recognized by modeling the digitized image from the CCD camera with perspective conversion.
However, the digitized image obtained by the CCD camera has an actual strain due to various factors. Thus, the model obtained by the perspective conversion is not exact. In order to overcome such a problem, it has been proposed to perform various corrections on the pick-up data to improve the precision of detection when the three-dimensional position of the object is to be sensed from the pick-up data.
For example, Onodera et. al., "Report of Research in Information Processing Institute", Vol. 92, No. 7, pp 115-118, January 1992 discloses a process of picking up a grid pattern on a flat plate positioned perpendicular to the optical axis of a camera and correcting the pick-up data. Such a process is intended to correct a strain due to aberration of the camera lens. An appropriate correcting function will be defined considering such a strain. The correcting function determines a coefficient on the comparison of the pick-up data for each pixel with the grid pattern which has been known with respect to its positional relationship in the three-dimensional space and also on the fact that the boundaries in the grid pattern are rectilinear. The correcting function is utilized to correct the pick-up data.
When the strain in an image picked up is corrected based on the relationship between the position of the image in the three-dimensional space and the position of the image in the picture, the position of the object can be recognized with relative exactness. However, the prior art requires the placing of an object to be picked up, such as a grid pattern, at a known location relative to the image pick-up device. In practice, it is difficult to position the grid pattern at the exact location, due to variations of the optical axis of the image pick-up device and so on. Thus, the prior art could not completely and exactly correct the pick-up data.